Receivables Receivables - Retrospective Review of Trouble Debt Restructuring (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011 Commercial Real Estate	Sep. 30, 2011 Consumer Loan Excluding Credit Card
Financing Receivable, Modifications [Line Items]
Increase in Trouble Debt Restructuring Loans	$ 1,000,000,000				$ 4,100,000,000	$ 717,000,000
Trouble Debt Restructuring Loans, Carried at Lower of Amortized Cost or Fair Value of Collateral Less Cost to Sell, Percent	0.37
Allowance for Loan and Lease Losses, Period Increase (Decrease)	40,000,000	(925,000,000)
Allowance for Loan and Lease Losses, Associated with Trouble Debt Restructuring		1,300,000,000
New TDR Loan Volume Upon Adoption of New Accounting Standards Update [Abstract]
Financing Receivable, Modifications, Interest Rate Modifications		1,400,000,000	1,814,000,000	3,630,000,000
Financing Receivable, Modifications, Trial Modificiations		200,000,000
Financing Receivable, Modifications, Re Ages		3,200,000,000	2,044,000,000	4,198,000,000
Financing Receivable, Modifications, Amount		$ 4,800,000,000